Quiescent

A cell state of a cellular automaton is said to be quiescent if the whole universe, when initialized to this state at generation 0, will remain in the same state in generation 1.

x = 5, y = 6, rule = LifeHistory F3$.3C$2.C$2.3C! #C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]] #C [[ ZOOM 20 AUTOSTART GPS 5 T 0 PAUSE 2 T 27 PAUSE 2 LOOP 37 ]]

Herschel-to-glider on LifeHistory that uses a Quiescent grey cell. This grey cell kills and living cells adjacent to it, and is considered dead. (click above to open LifeViewer)